For minimally processed vegetables, manufacturers should demonstrate that Listeria monocytogenes (Lm) levels will not exceed 100 cfu/g during shelf life. Challenge tests provide information on the growth behavior of Lm on a product. Technical guidance at EU level describes the use of Lm reference strain(s) from a characterized strain set. This strain set does not include isolates from vegetable products. Information on maximum growth rates of Lm strains isolated from vegetable products can be used for selection of relevant strains in challenge test and allows for more accurate prediction of expected cell numbers in growth models.
About the research
A set of 37 Lm strains previously isolated from vegetable products or its process environment were characterized for maximum growth rate at 8°C in a culture broth and for a selection of strains on iceberg lettuce. Experimentally determined growth rates were compared to data from literature and are in line with those reported for leafy greens.
Relevance for the sector
Growth rates of Listeria monocytogenes isolates from vegetables have been determined in broth and on iceberg lettuce and can be used for more accurate prediction of growth on minimally processed vegetables.